The present invention relates generally to the recording of moving images by means of a portable communication device. More particularly the invention relates to a method of producing an enhanced image of a relevant object recorded by a video camera.
The increasing capacities to transport high bandwidth signals in the fixed and mobile communication networks make mobile video telephony an increasingly viable application. A mobile videophone typically includes means for recording a movable image of the phone's user and means for presenting a corresponding movable image of at least one other person with whom the user communicates.
Audio information, for instance in the form of voice signals, is normally also communicated during a mobile videophone call. Therefore, means for duplex communication of audio information are also included in the videophone. Since the image recording means in the videophone requires that the videophone (or at least a device thereof including a camera, which typically is the main device) be placed at a particular minimum distance from the user, the sound information cannot be recorded by a regular microphone, such as those used in standard audio telephones.
The sound information must instead be exchanged between the user and main device either by means of a voice controlled microphone-loudspeaker arrangement or by means of a headset, which includes a microphone (positioned in proximity of the user's mouth) for receiving audio information and at least one earpiece (positioned in proximity of the user's ear(s)) for transmission of audio information to the user. A headset provides a higher degree of privacy than the microphone-loudspeaker arrangement. In most cases, the headset also provides a higher audio quality. The headset may, of course, prove impractical for certain applications. Wireless headsets (e.g. communicating via a Bluetooth interface), nevertheless, overcome the majority of the limitations associated with cable-connected headsets.
Consequently, there exit satisfying solutions for communicating voice signals also via mobile videophones. Unfortunately, there are yet no sufficiently good solutions for recording a moving image of the videophone user.
It is generally desirable that an object regarded as relevant for the videophone call (i.e. in most cases the face of the user) is recorded in such manner that it covers a substantial part of the available image area.
During a call the videophone user may either hold the videophone in his/her hand and point the phone's camera in the general direction of his/her face or alternatively place the phone on a stationary object in front of him/her in such manner that phone's camera is able to record images the user's face. In the first case movements of the user's hand and or upper body may cause the user's head to occasionally (at least partly) fall out of picture (i.e. outside the video camera's angular recording range). In any circumstances, the image of the user will most probably be more or less shaky. In the second case the image is inclined to be more stable, however, the risk that the user moves out of picture is at least as large as in the former case, particularly since the camera has a comparatively narrow angular recording range in order to fulfil the requirement that the relevant object should cover a relatively large part of the total image area. The measures previously taken to alleviate these problems involve the following three techniques.
A first alternative is to digitally analyse an image recorded by a video camera and create a stabilized image by processing a series of consecutively recorded image frames, extracting image features that are estimated to represent relevant information and generating enhanced moving images in which, for instance, the effects of shakes are reduced. This solution is based on complex calculations and hence demands a high processing capacity. That, in turn, means high costs and/or high power consumption. Furthermore, it is not certain that the image processing algorithms detect the correct relevant information and thus enhance the moving images in a desirable manner.
A second alternative to decrease the effects of shakes is to stabilize the camera in the videophone mechanically. This, however, either implies a bulky arrangement including a multitude of engines and complex levers or weights of impractical magnitude to be included in the videophone. Therefore, this solution is not interesting from a practical point of view.
A third alternative to decrease the effect of shakes is to attach the videophone camera to a rod, which is connected to a helmet worn by the user. This is, no doubt, an efficient way to produce a stable stabile image of user's face. Nevertheless, the solution is not likely to attain a high consumer interest, since the solution will probably be perceived as impractical and not very discrete.
The patent literature includes a few examples of applications outside the field of video communication in which headsets are used to adaptively convey information to a user. These examples are not directly related to the field of the present invention. However, they touch upon problems and solutions that are related to some aspects of the present invention.
For instance, the U.S. Pat. No. 4,866,229 discloses an apparatus for transmitting optical information from an essentially stationary transmitter to a viewer's movable headset. The solution is typically used to superimpose map information on directly observable information in the surroundings of an aircraft pilot. The transmitter tracks the headset and directs its optical information beam to the headset by means of a light source and a tracking guide sensor in the transmitter respective a tracking guide reflector in the headset.
The patent document JP, A, 8102702 describes a radio signal transmission system in which a headset includes two radio transmitters for producing radio signals with horizontal and vertical waveform directivity respectively. A detection device, which receives the radio signals from the headset, determines the orientation of the headset on basis of the different strengths of the respective radio signals.
The U.S. Pat. No. 5,619,582 discloses a system for enhancement of audio information in a concert environment involving a wireless headphone system. Multiple radio channels are transmitted to the audience of which all channels contain the same acoustic signal, however for each channel the signal is delayed by a different preset time period. The time of arrival of at least two radio frequency pulses are compared in order to locate the position of a particular headphone receiver in relation to the transmitter. On basis of this position the headphone receiver chooses a suitably delayed radio channel such that the decoded audio signal is approximately in phase with the sound arriving from the main speakers at the stage.
Despite the fact that the videophone communication technology and mobile communication solutions have been known for decades there still exists no example of a mobile videophone solution, which is both capable of producing and maintaining a stable image of a relevant object and is attractive to a user from a practical point of view.